US4156614A - Alumina-based ceramics for core materials - Google Patents

Alumina-based ceramics for core materials Download PDF

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Publication number
US4156614A
US4156614A US05/839,990 US83999077A US4156614A US 4156614 A US4156614 A US 4156614A US 83999077 A US83999077 A US 83999077A US 4156614 A US4156614 A US 4156614A
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alumina
ceramic
fired
core
ceramic material
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US05/839,990
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Charles D. Greskovich
Robert C. DeVries
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General Electric Co
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General Electric Co
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Priority to US05/839,990 priority Critical patent/US4156614A/en
Priority to JP9416878A priority patent/JPS5455013A/en
Priority to EP78101012A priority patent/EP0001434A1/en
Priority to IT28255/78A priority patent/IT1099621B/en
Priority to NO783375A priority patent/NO783375L/en
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    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/01—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics
    • C04B35/10—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics based on aluminium oxide
    • C04B35/111—Fine ceramics
    • C04B35/113—Fine ceramics based on beta-aluminium oxide
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22C—FOUNDRY MOULDING
    • B22C1/00—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/01—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics
    • C04B35/10—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics based on aluminium oxide
    • C04B35/101—Refractories from grain sized mixtures

Definitions

  • This invention relates to materials suitable for making cores for casting directionally solidified eutectic and superalloy materials.
  • Jet engines are a multi-million dollar business. The maximum operating temperature of these engines must be increased to attain higher efficiencies. Higher operating temperatures require the fabrication of new alloys with high temperature strength, toughness and corrosion resistance.
  • the most promising method of fabricating the turbine blade components with improved high temperature properties is by directional solidification (DS).
  • DS directional solidification
  • the rate of production of blades by the DS process is partly governed by the liquidus temperature which should be as high as possible.
  • the liquidus temperature of many of the promising alloy compositions being explored at this time is greater than 1500° C. and reaches nearly 1800° C. or higher.
  • the alloy is solidified around a ceramic core material which is subsequently leached away, leaving behind the proper air cooling cavities in the blade.
  • fused silica is the standard core material used at temperatures up to about 1550° C. without deleterious reaction with many of the alloy compositions.
  • silica cores are severely attached by one or more of the most reactive elements (A1, Hf, C) of the alloy. Consequently, silica cores cannot be used at the high temperatures required to directionally solidify the alloy. MgO and Y 2 O 3 cores are found to react only slightly with the aluminum in the alloy during DS at temperatures near 1800° C., but both materials have relatively poor leachabilities.
  • leachability and nonreactivity with the alloy up to 1800° C. are the two primary characteristics of the core material, other desirable characteristics are that it (1) be economical, (2) not undergo more than an overall dimensional change of ⁇ 2-4%, (3) have a porosity of from about 25% to about 60% to aid degassing during DS and increase the rate of leachability, (4) exhibit a modulus of rupture of only about 100 psi so that good crushability of the core occurs after the metal is cast, and (5) have good thermal shock resistance.
  • Another object of this invention is to provide a new and improved material composition for making ceramic cores which is also economical for use in casting directionally solidified eutectic alloys and superalloy materials.
  • a further object of this invention is to provide a new and improved material composition for making ceramic cores having increased porosity, leachability and crushability characteristics.
  • a fired ceramic compact suitable for use in a core in the casting and directional solidification of eutectic alloys and superalloy materials.
  • the ceramic material is an alumina-based material such as ⁇ -alumina, Na 2 O . 9A1 2 O 3 - Na 2 O . 11Al 2 O 3 , and other choice candidate materials such as CaO . 6Al 2 O 3 , SrO . 6A1 2 O 3 and BaO . 6Al 2 O 3 .
  • the ceramic material after firing is characterized by an interconnected network of porosity and solid phase.
  • the density of the fired compact is from about 40% to about 75%.
  • a desirable material composition can also be produced by admixing up to about 40 parts by weight of pure alumina to each of the alumina-based ceramic compounds and form in situ the interconnected network in which may be found a dispersion of particles of alumina within a matrix of alumina-based compounds.
  • Cores made of alumina-based ceramics of this invention are easily removed from the cast metal by autoclave leaching techniques embodying solutions of KOH or NaOH.
  • the ⁇ -aluminates, Na 2 O ⁇ 9Al 2 O 3 - Na 2 O ⁇ 11Al 2 O 3 are desirable for making the ceramic cores because of their excellent leaching characteristics.
  • Alumina-based compounds such as Na 2 O ⁇ 9Al 2 O 3 - Na 2 O ⁇ 11Al 2 O 3 , CaO ⁇ 6Al 2 O 3 , SrO ⁇ 6Al 2 O 3 and BaO . 6Al 2 O 3 have been discovered to be suitable materials for use in making cores for use in casting directionally solidified eutectic alloy and superalloy materials. All of these materials have a minimum temperature at which a liquid phase forms between the compound and alumina (Al.sub. 2 O 3 ) which is greater than 1800° C. which is the predicted maximum temperature that will be imposed upon the ceramic core material during directional solidification.
  • the alumina-based compounds may comprise at least in part the ceramic material composition used in preparing a ceramic core from the composition.
  • the material composition may consist essentially of 100 parts by weight of an individual alumina-based compound. Alternately the composition may comprise a two phase mixture of from about 60 parts by weight to 100 parts by weight of the alumina-based compounds, balance alumina.
  • a continuous phase of the alumina-based ceramic compound is formed in situ which provides either an interconnected network of solid and porous phases or a dispersion of particles of alumina within a porous matrix of alumina-based compounds.
  • Fired compacts of any of these material compositions when employed as cores in the casting and directional solidification of eutectic and superalloy materials, are easily removed therefrom by a caustic autoclave processing technique. Removal is achieved by leaching away the interconnected network of the alumina-based ceramic compound with a caustic agent of either a KOH or a NaOH solution.
  • Another particular feature of material compositions embodying two phase ceramic cores is that the activity of the alumina in the core is nearly equal to that of pure alumina.
  • the activity of the other oxide constituent in the phase mixture such, for example as Na 2 O, is considerably reduced so as to decrease its volatility to decrease its possible reactivity with the superalloy melt.
  • Cores made from material compositions including one or more of these sodium aluminates are leachable in a 20% KOH or NaOH aqueous solution at from 200° C. to 350° C. in an autoclave.
  • the process is economical and fairly fast, the leaching rate being on the order of from 0.5 to 1.0 centimeters per hour.
  • the material composition for core making is prepared by mixing the materials together mechanically. A sufficient amount of the material composition, with or without a binder material admixed therein, is placed in a mold and pressed to a green compact having a desired configuration. The green compact is fired at a temperature of from 1600° C. to 1800° C. to form the core whose material is characterized by a continuous phase of alumina-based ceramic compound formed in situ by sintering.
  • the material structure is characterized by either an interconnected network of solid and porous phases or particles of alumina within a porous matrix of alumina-based compounds.
  • the density of the fired compact varies with the particle size of the materials employed. For a range of particle size of from about 1 micron to about 50 microns, the density of the fired compact ranges from about 40 percent to about 75 percent.
  • a core 8 cm + 0.6 cm was made of substantially 100 parts by weight ⁇ -alumina material (Na 2 O ⁇ 9A1 2 O 3 ).
  • the average particle size of the material used was about 35 microns for a particle size distribution ranging between 5 and 50 microns.
  • the compact was formed at a pressure of 10,000 psi and fired at 1800° C. ⁇ 10° C. to sinter the compact for ease of handling.
  • the density of the sintered rod was 55 percent.
  • a melt of NiTaC-13 alloy was prepared, cast about the rod and directionally solidified thereabout at a temperature of 1675° C. ⁇ 25° C. for 20 hours in a controlled atmosphere of 10% CO by volume of argon gas.
  • the alloy composition, as cast was as follows:

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Ceramic Engineering (AREA)
  • Materials Engineering (AREA)
  • Manufacturing & Machinery (AREA)
  • Structural Engineering (AREA)
  • Organic Chemistry (AREA)
  • Mechanical Engineering (AREA)
  • Compositions Of Oxide Ceramics (AREA)
  • Mold Materials And Core Materials (AREA)
  • Porous Artificial Stone Or Porous Ceramic Products (AREA)
  • Ceramic Products (AREA)

Abstract

Cores made of alumina-based ceramics, such as β-alumina materials, are substantially non-reactive with directionally solidified eutectic and superalloy materials, do not cause hot cracking of the same, and are easily leachable from the cast metal.

Description

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to materials suitable for making cores for casting directionally solidified eutectic and superalloy materials.
2. Description of the Prior Art
Jet engines are a multi-million dollar business. The maximum operating temperature of these engines must be increased to attain higher efficiencies. Higher operating temperatures require the fabrication of new alloys with high temperature strength, toughness and corrosion resistance.
The most promising method of fabricating the turbine blade components with improved high temperature properties is by directional solidification (DS). The rate of production of blades by the DS process is partly governed by the liquidus temperature which should be as high as possible. The liquidus temperature of many of the promising alloy compositions being explored at this time is greater than 1500° C. and reaches nearly 1800° C. or higher. In order to make "hollowed" blades (which are mandatory for use in jet engines), the alloy is solidified around a ceramic core material which is subsequently leached away, leaving behind the proper air cooling cavities in the blade. Thus far, fused silica is the standard core material used at temperatures up to about 1550° C. without deleterious reaction with many of the alloy compositions. At temperatures exceeding about 1550° C., silica cores are severely attached by one or more of the most reactive elements (A1, Hf, C) of the alloy. Consequently, silica cores cannot be used at the high temperatures required to directionally solidify the alloy. MgO and Y2 O3 cores are found to react only slightly with the aluminum in the alloy during DS at temperatures near 1800° C., but both materials have relatively poor leachabilities.
Although leachability and nonreactivity with the alloy up to 1800° C. are the two primary characteristics of the core material, other desirable characteristics are that it (1) be economical, (2) not undergo more than an overall dimensional change of ˜2-4%, (3) have a porosity of from about 25% to about 60% to aid degassing during DS and increase the rate of leachability, (4) exhibit a modulus of rupture of only about 100 psi so that good crushability of the core occurs after the metal is cast, and (5) have good thermal shock resistance.
Considerable data compiled to data on the reactivity between ceramic core materials and nickel-base superalloy materials reveals that the major chemical reaction that occurs is between the ceramic and alumina (Al2 O3). The alumina comes primarily from the oxidation of some of the aluminum which is present in the superalloy composition. Since casting of the superalloy materials is practiced up to about 1800° C., the eutectic temperature of the ceramic compound and the alumina (Al2 O3) should be higher than 1800° C.
It is therefore an object of this invention to provide a new and improved material composition for making ceramic cores for directional solidification of eutectic alloy and superalloy materials.
Another object of this invention is to provide a new and improved material composition for making ceramic cores which is also economical for use in casting directionally solidified eutectic alloys and superalloy materials.
A further object of this invention is to provide a new and improved material composition for making ceramic cores having increased porosity, leachability and crushability characteristics.
Other objects of this invention will, in part, be obvious and will, in part, appear hereinafter.
BRIEF DESCRIPTION OF THE INVENTION
In accordance with the teachings of this invention there is provided a fired ceramic compact suitable for use in a core in the casting and directional solidification of eutectic alloys and superalloy materials. The ceramic material is an alumina-based material such as β-alumina, Na2 O . 9A12 O3 - Na2 O . 11Al2 O3, and other choice candidate materials such as CaO . 6Al2 O3, SrO . 6A12 O3 and BaO . 6Al2 O3 . The ceramic material after firing is characterized by an interconnected network of porosity and solid phase. The density of the fired compact is from about 40% to about 75%.
A desirable material composition can also be produced by admixing up to about 40 parts by weight of pure alumina to each of the alumina-based ceramic compounds and form in situ the interconnected network in which may be found a dispersion of particles of alumina within a matrix of alumina-based compounds.
Cores made of alumina-based ceramics of this invention are easily removed from the cast metal by autoclave leaching techniques embodying solutions of KOH or NaOH. In particular the β-aluminates, Na2 O · 9Al2 O3 - Na2 O · 11Al2 O3, are desirable for making the ceramic cores because of their excellent leaching characteristics.
All of the above-identified materials have been found to have little reaction with the cast metal. Cores made therefrom have shown excellent resistance to penetration of the cast metal.
DESCRIPTION OF THE INVENTION
Alumina-based compounds such as Na2 O · 9Al2 O3 - Na2 O · 11Al2 O3, CaO · 6Al2 O3, SrO · 6Al2 O3 and BaO . 6Al2 O3 have been discovered to be suitable materials for use in making cores for use in casting directionally solidified eutectic alloy and superalloy materials. All of these materials have a minimum temperature at which a liquid phase forms between the compound and alumina (Al.sub. 2 O3) which is greater than 1800° C. which is the predicted maximum temperature that will be imposed upon the ceramic core material during directional solidification. The alumina-based compounds may comprise at least in part the ceramic material composition used in preparing a ceramic core from the composition. The material composition may consist essentially of 100 parts by weight of an individual alumina-based compound. Alternately the composition may comprise a two phase mixture of from about 60 parts by weight to 100 parts by weight of the alumina-based compounds, balance alumina. When a compact of the material composition is fired to make the core, a continuous phase of the alumina-based ceramic compound is formed in situ which provides either an interconnected network of solid and porous phases or a dispersion of particles of alumina within a porous matrix of alumina-based compounds.
Fired compacts of any of these material compositions, when employed as cores in the casting and directional solidification of eutectic and superalloy materials, are easily removed therefrom by a caustic autoclave processing technique. Removal is achieved by leaching away the interconnected network of the alumina-based ceramic compound with a caustic agent of either a KOH or a NaOH solution.
Another particular feature of material compositions embodying two phase ceramic cores is that the activity of the alumina in the core is nearly equal to that of pure alumina. The activity of the other oxide constituent in the phase mixture, such, for example as Na2 O, is considerably reduced so as to decrease its volatility to decrease its possible reactivity with the superalloy melt.
The sodium aluminates and their solid solutions in the compositional range described heretofore, also known as β-alumina, are preferred for making the ceramic cores. Cores made from material compositions including one or more of these sodium aluminates are leachable in a 20% KOH or NaOH aqueous solution at from 200° C. to 350° C. in an autoclave. The process is economical and fairly fast, the leaching rate being on the order of from 0.5 to 1.0 centimeters per hour.
The material composition for core making is prepared by mixing the materials together mechanically. A sufficient amount of the material composition, with or without a binder material admixed therein, is placed in a mold and pressed to a green compact having a desired configuration. The green compact is fired at a temperature of from 1600° C. to 1800° C. to form the core whose material is characterized by a continuous phase of alumina-based ceramic compound formed in situ by sintering. The material structure is characterized by either an interconnected network of solid and porous phases or particles of alumina within a porous matrix of alumina-based compounds. The density of the fired compact varies with the particle size of the materials employed. For a range of particle size of from about 1 micron to about 50 microns, the density of the fired compact ranges from about 40 percent to about 75 percent.
To further illustrate the teachings of this invention, a core 8 cm + 0.6 cm was made of substantially 100 parts by weight β-alumina material (Na2 O · 9A12 O3). The average particle size of the material used was about 35 microns for a particle size distribution ranging between 5 and 50 microns. The compact was formed at a pressure of 10,000 psi and fired at 1800° C. ± 10° C. to sinter the compact for ease of handling. The density of the sintered rod was 55 percent. A melt of NiTaC-13 alloy was prepared, cast about the rod and directionally solidified thereabout at a temperature of 1675° C. ± 25° C. for 20 hours in a controlled atmosphere of 10% CO by volume of argon gas. The alloy composition, as cast, was as follows:
Nickel -- 63.4%
Chromium -- 4.4%
Cobalt -- 3.3%
Aluminum -- 5.4%
Tungsten -- 3.1%
Rhenium -- 6.2%
Vanadium -- 5.6%
Tantalum -- 8.1%
Carbon -- 0.48%
Upon completion of the directional solidification, examination of the mold-metal interface was made by means of a metallographic polished-section of the β-alumina-NiTaC alloy interface. A thin reaction zone, 10 microns in thickness was observed at the interface. The composition of the material of the reaction zone was α-Al.sub. 2 O3. No evidence of hot cracking was observed along the interface. The tantalum carbide strength reinforcing phase, approximate composition TaO.75 VO.25 C, was still present in the cast alloy matrix even at the β-alumina-NiTaC-13 interface. The formation of the thin reaction zone did not hinder the development of the carbide phase near the interface. Upon further examination, no significant penetration of the core had been made by the cast metal and the surface of the casting was commercially acceptable.

Claims (4)

We claim as our invention:
1. A fired ceramic core of a ceramic material suitable for use in the casting and directional solidification of superalloy and eutectic materials consisting essentially of a ceramic material which, before firing, consists of one alumina-based compound material having the general formula MO . NAl.sub. 2 O3, wherein M is Na2, Ca, Sr or Ba, and optionally up to 40 parts by weight of undoped alumina, the average particle size of the ceramic material being from about 1 to 50 microns,
the ceramic material, after firing, being characterized by a continuous phase of the alumina - based compound as an interconnected network defining a plurality of interstices in which undoped alumina grains are dispersed,
the density of the fired core is from about 40 percent to about 75 percent, the modulus of rupture is only about 100 psi, the minimum temperature at which a liquid phase forms between the compound and the alumina is greater than 1800° C.
2. The fired ceramic compact of claim 1 wherein
the ceramic material before firing is a two phase mixture which includes up to 40 parts by weight of undoped alumina admixed to the alumina-based compound material.
3. The fired ceramic compact of claim 1 wherein
M is Na2.
4. The fired ceramic compact of claim 2 wherein
M is Na2.
US05/839,990 1977-10-06 1977-10-06 Alumina-based ceramics for core materials Expired - Lifetime US4156614A (en)

Priority Applications (5)

Application Number Priority Date Filing Date Title
US05/839,990 US4156614A (en) 1977-10-06 1977-10-06 Alumina-based ceramics for core materials
JP9416878A JPS5455013A (en) 1977-10-06 1978-08-03 Ceramic based on coreemateriallgrade alumina
EP78101012A EP0001434A1 (en) 1977-10-06 1978-09-28 Alumina-based ceramics for core materials
IT28255/78A IT1099621B (en) 1977-10-06 1978-09-29 ALUMINUM-BASED CERAMICS FOR FOUNDRY SOUL MATERIALS
NO783375A NO783375L (en) 1977-10-06 1978-10-05 CERAMIC MATERIAL BASED ON ALUMINUM OXYD

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EP (1) EP0001434A1 (en)
JP (1) JPS5455013A (en)
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NO (1) NO783375L (en)

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US4480681A (en) * 1982-08-30 1984-11-06 Doulton Industrial Products Limited Refractory mould body and method of casting using the mould body
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US4837187A (en) * 1987-06-04 1989-06-06 Howmet Corporation Alumina-based core containing yttria
WO1989005204A1 (en) * 1987-12-08 1989-06-15 Harri Sahari Method for preparation of moulds and cores used in the casting of metals
US5129998A (en) * 1991-05-20 1992-07-14 Reynolds Metals Company Refractory hard metal shapes for aluminum production
US5336645A (en) * 1993-09-27 1994-08-09 Corning Incorporated Soluble, cellulated mold and foamable mixture
US5409871A (en) * 1993-11-02 1995-04-25 Pcc Airfoils, Inc. Ceramic material for use in casting reactive metals
US5545003A (en) * 1992-02-18 1996-08-13 Allison Engine Company, Inc Single-cast, high-temperature thin wall gas turbine component
US5552356A (en) * 1994-07-11 1996-09-03 Bayer Ag Boron subphosphide/aluminum oxide composite materials, processes for the production thereof and use thereof
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US6494250B1 (en) 2001-05-14 2002-12-17 Howmet Research Corporation Impregnated alumina-based core and method
US20050269055A1 (en) * 1998-11-20 2005-12-08 Frasier Donald J Method and apparatus for production of a cast component
US20060243421A1 (en) * 2005-04-29 2006-11-02 United States Of America, Represented By Secretary Of The U.S. Army Soluble casting core for metal matrix composite components and method of producing thereof
US20080135204A1 (en) * 1998-11-20 2008-06-12 Frasier Donald J Method and apparatus for production of a cast component
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JPS62153158A (en) * 1985-08-30 1987-07-08 東洋シーシーアイ株式会社 Heat resistant composition and manufacture
US4771028A (en) * 1985-08-30 1988-09-13 Catalysts And Chemicals Inc. Heat resistant composition and method of producing the same
JPS63242917A (en) * 1987-03-27 1988-10-07 Agency Of Ind Science & Technol Production of heat resistant alumina complex oxide
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IT7828255A0 (en) 1978-09-29

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